Looks more certain that the derailment was caused by the train being overspeed passing through a turnout from the main running line to a loop line.
Indeed. Though whether it was driver, pilotman, signalman error, a fault with the signalling system or permanent way, something else, or a combination or misunderstanding, we have yet to learn. Lots on the video, including concerns about the state the railway is in near where that accident happened.
Remarkable strength of an XPT (Australian
HST▸ derivative) that it came off at around 80kph on a 15kph turnout, the whole train jackknifed behind the leading power car and only the two in the front cab died. 157 passengers on board, just 11 injured only one seriously (but not life threatening).